Since my update to latest wordpress 5.4.1 I cannot login an more

If I try to login, I get redirected to the login page without error message.
I was only able to login after moving the pressbooks folder in the backend to a different location which brought up the wordpress login mask. After login I moved the pressbooks folder back bringing back Pressbooks. But after logout and trying to login again, the same problem occurs. Does that ring a bell with anybody?
I am getting redirected to
https://pressbooks.delivros.ch/wp-login.php?redirect_to=https%3A%2F%2Fpressbooks.delivros.ch%2Fwp-admin%2F&reauth=1

After a good bit of sweatting I think I found the origin of the redirect issue in my installation: LTI Provider Version 1.4.0-dev
That LTI provider version was shown to me in my Pressbooks site as an available update. Dektivating the plugin solces the issue. Activating it brings back the issue. So I think the LTI provider Version 1.4.0-dev causes the redirect issue.

I now went back to LTI provider 1.3.1
What I noted:
If you install LTI 1.3.1 it lists LTI 1.4.0-dev in Pressbooks as an update (see below)
If you install LTI 1.3.2 it lists it as LTI 1.4.0-dev in Pressbooks